The present invention pertains to a self releasing holddown mechanism for a self elevating dock leveler.
Dock levelers or so-called dockboards are widely used in conjunction with freight vehicle loading docks and the like to provide a continuous path between the loading dock and the loadbed of a vehicle. Dock levelers typically utilize one or more heavy duty springs or other means which operate through a linkage to bias the dock leveler ramp from a stored position to an elevated position, including the engaged or working position of the leveler with respect to a vehicle loadbed. In dock levelers of the general type mentioned above, a holddown mechanism is utilized to maintain the dock leveler in the stored position or a desired working position against pivotal movement, except within a very limited range, about the ramp pivot axis during operation or storage.
One type of holddown mechanism which enjoys certain advantages is disclosed and claimed in U.S. Pat. No. 6,061,859 to Bruce R. Winter and assigned to the assignee of the present invention. The dock leveler holddown mechanism disclosed and claimed in the aforementioned patent includes a ratchet bar and pawl mechanism together with a self-releasing feature to minimize the chance of damage to or failure of the holddown mechanism. However, it has been deemed desirable to further improve the general type of holddown mechanism disclosed and claimed in U.S. Pat. No. 6,061,859. It is to these ends that the present invention has been developed.
The present invention provides an improved holddown mechanism for a dock leveler or dockboard, particularly of the type which has a biasing mechanism tending to move the leveler ramp to an elevated position.
The present invention also provides a holddown mechanism for a dock leveler ramp which is self-releasing to minimize the risk of damage to or failure of the holddown mechanism or the ramp as a consequence of movement of a vehicle loadbed during loading and unloading operations. In a preferred embodiment of the holddown mechanism, an elongated bar is connected to the dock leveler ramp and is engaged with a roller type lock member which is operable to prevent movement of the bar and the ramp in an upward direction except over a limited ranged provided by the holddown mechanism. If movement of the ramp exceeds the range of movement provided by the holddown mechanism, the lock member releases the bar to allow the ramp to move upward and to prevent damage to the ramp and/or the holddown mechanism.
The combination of the bar and roller lock member improves the operating life and the performance of the holddown mechanism and reduces the chance of damage to the bar, the bar lock member, and other parts of the holddown mechanism as compared with holddown mechanisms which utilize a ratchet and pawl, for example. The holddown mechanism of the present invention also includes an improved arrangement of an actuator member for engaging and releasing the lock member with respect to the bar and an improved self releasing mechanism for releasing the roller lock member from forcible engagement with the bar to allow movement of the dock leveler ramp.
Those skilled in the art will further appreciate the advantages and superior features of the invention upon reading the detailed description which follows in conjunction with the drawing.